Process and device to piece back to a spinning device operating with a pneumatic torsion element

ABSTRACT

For piecing to a spinning device operating with a pneumatic torsion element, yarn is fed back through the torsion element into a readiness position alongside a drafting mechanism, while the roving is stopped before the end of the drafting zone. The roving is then released, whereby the forward roving end which is leaving the drafting mechanism, and which typically is rendered unsuitable for piecing due to stoppage of the roving, is sucked off. When a roving segment which remained in the drafting mechanism during the prior roving stoppage has been taken away, the roving and the yarn end are brought together and are simultaneously fed to the torsion element so as to be combined. To carry out this process, the drafting mechanism preferably includes before the end of its drafting zone at least one roving stopping device which may be controllable with feedback from a yarn monitor located adjacent the path of yarn being conveyed to a yarn take-up mechanism, such as a bobbin. Furthermore, a suction nozzle can be selectively situated and activated between a pair of exit rolls of the drafting mechanism and the torsion element, for removing controllably the forward end of a roving rendered unsuitable for piecing by stoppage of such roving.

BACKGROUND AND SUMMARY OF THE INVENTION

The instant invention relates to a process for piecing back to aspinning device operating with a pneumatic torsion element in which ayarn which is fed back to a drafting mechanism is brought together witha roving, as well as to a device to carry out the process.

In a known process of this type the pair of intake rolls of the draftingmechanism is stopped for the purpose of piecing back when a yarnbreakage occurs, so that the roving or the fiber sliver is opened in thedrafting zone which follows this pair of intake rolls (DE-OS 3,411,577and 3,413,894 corresponding with U.S. Pat. Nos. 4,550,560 and 4,545,193,respectively). When the fiber sliver or the roving is fed back to thetorsion element for piecing, an irregularity is produced which must beremoved from the finished yarn in a further step.

It is therefore the objective of the instant invention to create aprocess and a device which makes it possible to produce an unobtrusivepiecing joint with little expenditure.

This objective is achieved according to the invention in that theroving, after being stopped, is at first released for the piecingprocess and in that the forward end of the roving which is leaving thedrafting mechanism is sucked away until the roving segment which hasremained in the drafting mechanism during the prior stoppage of theroving has been taken away, and in that the roving is subsequently fedto the torsion element while being simultaneously brought together andcombined with the yarn end. Due to the stoppage of the roving or of thefiber sliver said roving or said fiber sliver is not only discontinued,but its forward end is given an irregular shape which is unsuitable forpiecing. Therefore the removal of this affected forward end of theroving or sliver ensures that in piecing a segment with unaffected fiberorientation and length is fed to the torsion element to be combined withthe yarn. In this way, even and unobtrusive piecing joints are obtained.

In the sense of the instant invention, roving is understood to be anysliver-like material which can be fed to the torsion element by means ofa drafting mechanism, regardless of whether it has little torsion ornot. Not only flyer rovings but also card slivers etc. fall thereforeinto this category.

In order to coordinate the re-starting of yarn torsion in a particularlysimple manner with the beginning of yarn draw-off, whereby the length ofthe piecing joint can be predetermined precisely, it is preferable todraw off the yarn at first through the torsion element without itexerting any twisting action upon the yarn, whereby furthermore, infunction of the position of the end of the yarn previously fed-back, theremoval of the roving is ended and the feeding of the roving to thetorsion element is started, roving and yarn now being submitted togetherto the twisting effect which now begins.

It is basically sufficient if the yarn and the stretched roving areallowed to run together into the twisting nozzle. However, the longerthe common conveying path of roving and yarn between drafting mechanismand torsion element, the better the piecing joint. For this reasonprovisions can be made in a preferred embodiment of the inventiveprocess for the yarn to be introduced laterally into the closed clampingline of the two output rolls and to be fed necessarily to the torsionelement at the speed determined by the rotational speed of the twooutput rolls.

To prevent the injector effect in the torsion element from provokinguncontrolled draw-off of the yarn after the feeding of compressed air isresumed provisions are made in a preferred version of the process forthe yarn which is brought together with the roving to be retainedpneumatically and to be furthermore braked mechanically upon resumptionof yarn draw-off until part of it is brought together with the roving.The yarn is thus drawn off at a draw-off speed which is dictatedmechanically by the winding device or by a pair of draw-off rolls.Beyond this, the yarn in the process of draw-off is controlled betweenyarn holding device and torsion element until further controlled yarndraw-off is ensured by bringing together the yarn and the roving.Perfect and unobtrusive piecing joints are ensured in this way.

The success of the piecing process does not only depend upon the stateof the forward end of the roving but also upon the state of the yarnend. For this reason it is advisable for the end of the yarn which is tobe brought together with the roving to be subjected to a pre-treatmentbefore this joining together. This is done preferably by measuring outthe yarn to a defined length. The position of the yarn end in theprocess of being drawn off and which is thus brought to a determinedlength can then be sensed and can be used as a basis to control furtherphases of operations in the piecing process, for example in startingroving feeding, in controlling roving suction, in controlling compressedair feeding to the torsion element, etc.

To carry out the process the invention provides for the mouth of asuction nozzle to be brought into action alongside the conveying path ofthe fiber material between the two outlet rolls of the draftingmechanism and the torsion element. Before piecing the roving is notconveyed through the drafting mechanism but is stopped by the rovingstopping device. Depending upon the configuration of the roving stoppingdevice (for example a stoppable pair of intake rolls of the draftingmechanism or a roving clamping device) the forward end of the roving isgiven a form which makes it impossible to obtain an unobtrusive piecingjoint, so that said joint must be removed in a subsequent cleaningprocess. In order to avoid this, the instant invention provides, afterrelease of the roving, for the affected forward end of the roving to betaken away by means of the suction nozzle mouth which can be activatedalongside the conveying path of the fiber material, so that a faultlesssegment of roving then becomes available for piecing.

To be able to precisely synchronize the moment at which the spinningoverpressure in the torsion element is switched on with the moment whenyarn draw-off begins and when the negative pressure at the suctionnozzle is switched off, the suction nozzle and the torsion element canbe connected via a control device to a yarn-end supervision device whichis attributed to the pneumatic yarn holding device for this switchingoff of the negative pressure at the suction nozzle and switching on theoverpressure at the torsion element. In this way, a defined transfer ofthe forward end of the roving from the suction nozzle to the torsionelement is achieved, and this is essential for the obtention of goodpiecing joints.

To exclude uncontrolled yarn movement and uncontrolled start-up thereofthrough the pneumatic torsion element when the yarn running into thetorsion element is being held in a pneumatic yarn holding device, andthereby to avoid irregular piecing joints, this pneumatic yarn holdingdevice is advantageously associated with a yarn brake which acts uponthe yarn in the process of draw-off.

In order for the yarn to be fed back without interference, the yarnbrake is preferably controllable by means of a controlling device andcan be brought by said controlling device into or out of the path of theyarn extending into the yarn holding device. It is advantageous here, inorder to ensure faultless guidance of the yarn with respect to the yarnbrake, if said yarn brake is located in the yarn holding device which isfashioned as a suction pipe.

However, the quality of the piecing joints is not only influenced by theshape of the forward end of the roving but also by the shape of the yarnend. To ensure that not only a forward end of the roving of perfectquality but also a defined yarn end is available for piecing, apre-treatment device which can be used on the yarn is suitably providedin a further embodiment of the object of the invention. Thispre-treatment device is preferably made in the form of a yarn separatingdevice and is installed in the yarn holding device which is made in formof a suction pipe.

It is customary to carry out piecing with the help of a piecing carriagewhich can travel alongside the machine and which can be brought to anyspinning station at will. In this case the controlling device forpiecing is advantageously installed on the piecing carriage, especiallythe suction nozzle, the yarn holding device as well as a controllingdevice which can be brought to bear upon the roving stopping device.

To avoid that the pneumatic yarn holding device cover long distances orany distance at all during feed-back of the yarn, the torsion elementcan, in addition to a first set of compressed air bores with a directioncomponent in the direction of yarn draw-off and which are subjected tocompressed air during normal spinning operation, be furthermoreassociated with a second set of compressed air bores with a directioncomponent in feed-back direction and which are subjected to compressedair during the feed-back of the yarn into piecing position. The torsionelement is preferably associated with a first stop which determines thespinning position of the torsion element and which is provided with afirst compressed air feeding opening that can be connected to the firstset of compressed air openings, as well as with a second stop whichdetermines the threading position and which is provided with a secondcompressed air feeding opening which can be connected to the second setof compressed air openings.

Preferably each of the two compressed air feeding openings can beprovided with a check valve which can be opened by application of thetorsion element to the corresponding stop. The second stop is suitablyinstalled on a piecing carriage which can travel alongside the machineand can be brought to any spinning station at will.

To suck away the fly which is produced in continuous spinning operationand to take away a ruptured yarn segment, a preferred embodiment of theobject of invention is equipped with a suction nozzle after the torsionelement (as seen in spinning direction) near said torsion element anddirectly next to the yarn conveying path.

The invention ensures reliable piecing and unobtrusive piecing jointswith a device of simple design. Only orderly material is presented forpiecing, so that no danger exists for the torsion element to becomeclogged because of non-oriented fibers and consequently for yarnbreakage to be provoked.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinbelow with referenceto embodiments thereof illustrated in the accompanying drawings.

FIG. 1 shows a schematic side-view of a spinning device designedaccording to the invention;

FIG. 2 shows the spinning device of FIG. 1 in the threading/feed-backphase, in top-view;

FIG. 3 shows a detail of FIG. 2 in a side view;

FIG. 4 shows the part of the inventive device of FIG. 3 in the piecingphase;

FIG. 5 shows a cross-section of a torsion element as well as two stopsinteracting with the torsion element in its two end positions;

FIG. 6 shows a schematic side-view of a piecing device which iscontrolled from a service carriage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The design of the spinning device is first explained through FIG. 1. Inthe spinning device shown, a roving 1 or a fiber sliver is drawn to thedesired yarn thickness by means of a drafting mechanism 2 and is thenfed to a pneumatic torsion element 3 where the roving 1 or the fibersliver is spun into a yarn 10. Yarn 10 is drawn out of the torsionelement 3 by means of a pair of draw-off rolls 4 and is fed via a yarntension compensation hoop 52 to a winding device 5 where the yarn 10 iswound on a bobbin 50. Bobbin 50 is driven by a bobbin roll 51.

The drafting mechanism 2 shown as an example is equipped with four pairsof rolls with rolls 20/200, 21/210, 22/220 and 23/230. Before the rolls20, 200 of the first pair of rolls and between the rolls 20, 200-21,210-22, 220 of the first and second as well as of the second and thirdpair of rolls there are the compressors 201, 211 or 221, preventingexcessive spreading of the roving 1 in the drafting mechanism 2. Infront of the rolls 21, 210 of the third-before-last pair of rolls aswell as in front of the rolls 20, 200 of the pair of rolls upstream fromthese, the roving clamping devices 241 or 240 are installed and areassociated with a joint driving device 24.

The small belts 222 and 223 loop around the two rolls 22, 220.

A suction nozzle 6 is installed next to the conveying path of the fibermaterial between the rolls 23, 230 of the pair of output rolls of thedrafting mechanism 2 and the torsion element 3.

The yarn is imparted false torsion by the compressed air fed to thepneumatic torsion element through a controllable compressed air line 32,said false torsion being removed subsequently to a great extent. Forthis purpose the shown torsion element is equipped with an injectionnozzle 30 and a torsion nozzle 31 after it, carried by a joint holder33. As the false torsion is imparted and as it is removed the fiber endsare tied into the yarn core while loops are being formed and thus causea true core torsion to remain in the yarn so that the latter possessesthe desired strength.

The holder 33 is supported in a movable fashion so that the torsionelement 3 can be brought from a spinning position I into a threadingposition II and back again (FIG. 2).

The draw-off devices 4 consist as is usual of a driven draw-off roll 40and of a pressure roll 41 which can be lifted off from said draw-off 40roll and which is elastically pressed against it. On its way between thetorsion element 3 and the draw-off device 4, the yarn 10 is monitored bya yarn monitor 70 which ascertains the presence of spinning tension. Theyarn monitor 70 is controllably connected to drive 24 of the rovingclamping devices 240 and 241 in order to stop the roving 1 in case ofthread breakage, while rolls 20, 21, 22 and 23 of the drafting mechanism2 continue to run.

Directly next to the path of the yarn, near the torsion element 3,between the latter and the yarn monitor 70, is located the mouth of asuction nozzle 42. It is the role of this suction nozzle 42 to suck awayloose fibers which leave the torsion element 3 in form of fly when thespinning operation is interrupted.

When a yarn breakage occurs, the response of the thread monitor 70 andthe activation of the roving clamping devices 240, 241 cause the roving1 to be broken downstream from the roving clamping device 241 due to thecontinued running of the drafting mechanism 2. This portion of roving 1,which continues to be fed through the drafting mechanism 2 to thetorsion element 3 is spun into a short piece of yarn by said torsionelement 3 which continues to be subjected to overpressure. Since thisshort piece of yarn is no longer in contact with yarn 10 which is woundon bobbin 50 as a consequence of the yarn breakage, it is now suckedaway through suction nozzle 42.

Simultaneously with the occurrence of a yarn breakage, bobbin 50 islifted off from the bobbin roll 51 in a known manner (FIG. 3).

To piece the yarn, the swivelling holder 33 brings the torsion element 3out of spinning position I into threading position II (FIG. 2) where theintake opening of the injection nozzle 30 is located directly in frontof the mouth of a pneumatic yarn holding device 8. The spinningoverpressure in the torsion element 3 is furthermore switched off.

The yarn end is sucked away in known manner through a swivelling suctionpipe 91 (FIG. 6) from the bobbin 50 which is now driven in unwindingdirection. As soon as the yarn end inside suction pipe 91 has reached asufficient length, so that it is securely taken along by the suctionpipe 91 even when the latter is swivelled, the yarn holding device 8,fashioned as a suction pipe, is brought from the yarn transfer positionindicated by a broken line in FIG. 2 into a yarn receiving position nearthe outlet opening of the torsion element 3 which is now in threadingposition II. The yarn 10 which is held by suction pipe 91 is then cut inthe known manner, so that it is sucked through the torsion element 3upon subjection of the pneumatic yarn holding device 8 to negativepressure. Bobbin 50 is then stopped. If the transfer of yarn 10 to thepneumatic yarn holding device 8 is undertaken, reverse rotation ofbobbin 50 can also be interrupted earlier and temporarily.

As shown in FIG. 2, the end of yarn 10 which has been fed back is now ina position of readiness alongside to the drafting mechanism 2 which hasremained unaffected by the thread monitor 70 and therefore continues tobe driven as before, while roving 1 however has been stopped before thedrafting zone which is limited by the rolls 21, 210 and 22, 220.

The torsion element 3 is now brought back into its spinning position I(FIG. 4) while the pneumatic yarn holding device 8 is brought out of theyarn receiving position (indicated by a broken line in FIG. 4) shown inFIG. 2 and into the position indicated by an unbroken line in FIG. 4(yarn transfer position).

The suction nozzle 6 is now subjected to negative pressure. Roving 1 isthen released by the roving clamping devices 240 and 241. The forwardend of roving 1 has now a different form than during normal spinningoperation because of the interruption of said roving 1 which wasprovoked upon occurrence of the yarn breakage and is not, or only in alimited way, suitable for piecing. For this reason the forward end ofroving 1 is dissolved and sucked away by the negative pressureprevailing in suction nozzle 6 until a continuous flow of fiber materialis again ensured. The beginning of the drawn roving 1 is then introducedinto the torsion element 3 through discontinuance of the negativepressure at the suction nozzle 6 and resumption of overpressure in saidtorsion element 3 in which said roving 1 is combined with the yarn 10.The suction effect of the airstream produced in the torsion element 3also draws off yarn 10 from the pneumatic yarn holding device 8. Whilethe yarn end and the forward end of the roving are led together throughthe torsion element 3 they are combined.

In coordination with the release of roving 1 and with the resumption ofair pressure in the torsion element 3 the bobbin 50 is lowered once moreupon the bobbin roll 51. The draw-off tension which is now reestablishedcauses yarn 10 to be drawn into the clamping line of the pair ofdraw-off rolls 4. In this phase it is possible fo the pressure roll 41to be lifted off from the driven draw-off roll 40 until the threadmonitor registers that spinning tension has been reestablished.

The explained process as well as the described device can be modified inmany ways. The replacement of characteristics by equivalents and othercombinations thereof come within the framework of the instant invention.For example, instead of a drafting mechanism 2, with four pairs ofrolls, it is also possible to use a drafting mechanism with only threeor else with more than four pairs of rolls. In the latter instance aroving clamping device, fashioned in the conventional manner, is alsoinstalled before the third-before-last pair of rolls and before eachpair of rolls before it. The torsion element 3 can (as shown) consist ofan injector nozzle 30 and a twisting nozzle 31. For many purposeshowever, a single nozzle can be sufficient for the torsion element 3.

The roving stopping device can be fashioned in different ways. It ispossible, for example, to attribute a coupling to the pair of intakerolls in order to stop roll 20. A roving stopping device in form of aroving clamping device is by comparison simpler in construction whileaffording equal reliability of operation.

According to the process described in FIGS. 1 to 4 the yarn 10 isbrought into such a position by a movement that is axial as well ascrosswise to the axis of the torsion element 3 so that the yarn segmentwhich is stretched between the torsion element 3 and the pneumatic yarnholding device 8 is applied to the front of the roll 230 and isintroduced from the side into the clamping line of the pair of exitrolls formed by rolls 23, 230 when said roll 230 rotates. The yarn 10which is fed to the torsion element 3 is thus fed to said torsionelement at a speed which is determined by the rotation of said rolls 23,230. In this way, defined piecing conditions are obtained. To preventuncontrolled drawing-off of the yarn 10 from the pneumatic yarn holdingdevice 8 before its insertion into the clamping line of the pair of exitrolls, said yarn holding device 8 is equipped with a yarn brake 81 whichelastically retains the yarn 10 in the process of being drawn off. Yarn10 is then drawn off from yarn holding device 8 only at the speed whichit is given by bobbin 50 and/or by the pair of draw-off rolls 4. Thiscontributes to increased reliability in the piecing process.

As indicated in FIG. 2, it is often sufficient if the yarn is broughttogether with the roving 1 only at the entry into the torsion element 3.Uncontrolled drawing-off of the yarn 10 is prevented here too by theyarn brake 81.

In accordance with the embodiment indicated schematically in FIG. 6, theyarn brake 81 is made in form of a braking bolt 810 which is installedin the yarn holding device 8, fashioned as a suction pipe. Said brakingbolt can be moved crosswise to the said yarn holding device'slongitudinal axis and can be brought into contact with the oppositeinterior wall of said yarn holding device 8 by its stop surface which isequipped with a retaining clothing 811. Yarn 10 is braked mechanicallyby this yarn brake 81 until part of said yarn 10 has come into contactwith roving 1 and is by then in full piecing process inside torsionelement 3.

In order to obtain piecing joints of high quality a further variant ofthe process provides for the yarn end to be pieced to be given a definedform. For this reason the yarn end is subjected to a pre-treatment of aknown type. Here, the yarn end can be untwisted by means of apre-treatment device 82, it can be napped or simply be brought to adefined length by cutting.

FIG. 6 shows an example in which the pre-treatment device 82 is a yarncutting device and is installed inside the yarn holding device 8 whichis fashioned as a suction pipe.

In order to coordinate the beginning of the spinning process preciselywith the resumption of yarn draw-off, provisions are made according toFIG. 6 for the pneumatic yarn holding device 8 to be associated with ayarn-end monitoring device 83. This device, which is only shownschematically, is provided with a light source 830, as shown in FIG. 6,and with a photoelectric cell 831 which is connected to control device7. This control device 7 is connected to a valve 60 for the control ofthe underpressure in the suction nozzle 6 as well as to a valve 71 forthe control of the overpressure in the torsion element 3. Thus, when theyarn 10 which is drawn off from the pneumatic yarn holding device 8 bythe bobbin 50 and/or the draw-off device 4 reaches the light beamprojected by light source 830 towards photoelectric cell 831 in thecourse of piecing, said light beam is released. This causes the controldevice 7 to switch off the negative pressure at the suction nozzle 6 andto switch on the overpressure at the torsion element 3. Other steps ofoperation of the piecing process, for example the application of apressure roll 41 which has previously been lifted off from the drivendraw-off roll 40, can be controlled as a function of the position of theyarn end.

According to FIG. 6 the control device 7 is installed on a piecingcarriage 9 which can travel alongside the spinning machine to any one ofa plurality of spinning stations in order to piece the yarn to thelatter, as for example in order to repair yarn breakage.

To minimize construction expenses, all devices which are only neededduring the piecing process are installed on this piecing carriage 9. Inthe embodiment shown in FIG. 6, the most essential of these elements arethe suction nozzle 6 which sucks away the forward end of the roving andthe pneumatic yarn holding device 8 with all devices which areassociated therewith. Furthermore, the control device 7 can becontrollingly connected with the driving device 24 for the rovingstopping device, as is indicated schematically by a plug-in connection72. Instead of the indicated plug-in connection 72 (or 710, for thevalve 71 which is attributed to the torsion element 3) it is alsopossible to provide a different type of connection. For example, thepiecing carriage 9 is constantly connected to the spinning machine viatrailing cables (not shown) and is connected via an appropriate electricswitch to each spinning station as it is being serviced.

As FIG. 6 shows, the control device 7 is controllably connected to abobbin support and drive device 90. This device holds the bobbin 50 at adistance from the bobbin roll 51 during piecing and is turned back sothat yarn 10 is fed back into the suction pipe 91. At the same time thebobbin support device and the bobbin drive device can also be elementswhich are independent of each other. The swivelling drive (not shown) aswell as the control valve 910 for the suction pipe 91 are alsocontrollingly connected to the control device 7. In addition to theabovementioned elements, a control valve 80 for the yarn holding device8 and the drives 810 and 820 for the yarn brake 81 and the pre-treatmentequipment 82 are also connected to the control device 7.

Furthermore the torsion element 3 is moved in and out of the spinningposition I under control of the control device 7 in a manner which isnot shown here.

The operation of the device shown in FIG. 6 is described below:

During piecing, the roving 1 is first of all released in the mannerdescribed and is taken away by the negative pressure prevailing at thesuction pipe 6 after it leaves the pair of exit rolls constituted by therolls 23, 230 of the drafting mechanism 2.

Furthermore, the yarn end being retained by the yarn holding device 8 isgiven a defined form, for example by brushing or by cutting the yarn endto a predetermined length.

In synchronization with this, yarn 10 is drawn off through the torsionelement 3 by lowering the bobbin 50 on the bobbin roll 51 and/or byapplying the pressure roll 41 on the draw-off roll 40 through theclamping of said yarn which is thus carried out. At this moment thetorsion element 3 is however not yet subjected to any overpressure, sothat no twisting action is exerted upon the yarn 10. While the yarn isthus drawn off from the yarn holding device 8 the yarn brake 81 is inits braking position in which the yarn is braked between the inner wallof the yarn holding device 8 and the retention clothing 811 which iselastically applied to said inner wall, so that uncontrolled draw-off ofyarn 10 from the yarn holding device 8 is not possible.

When the yarn end now reaches the yarn end monitoring device 83, thenegative pressure at the suction pipe 6 is switched off and theoverpressure at the torsion element 3 is switched on in function of thisposition being reached, so that the removal of the roving 1 isterminated and so that said roving 1 is instead now fed to the torsionelement 3. Due to the twisting effect which now takes place, the yarnend and the drawn roving 1 are now twisted into a yarn 10.

FIG. 5 shows a torsion element 3 which, for reasons of clarity, is shownturned around its longitudinal axis by 90° as compared with the torsionelement 3 shown in FIGS. 1 to 4. By its configuration, the torsionelement 3 shown in FIG. 5 makes it possible for the yarn holding device8 to execute merely a very simple movement or to be even stationary. Thetorsion element 3 in this case, in addition to a first set of compressedair bores 300 and 310 with a direction component in the direction ofyarn draw-off (arrow 11), is furthermore provided with a second set ofcompressed air bores 301 and 311 with a direction component in thedirection of feed-back. The first set of compressed air bores 300 and310 is subjected to compressed air during spinning while the second setof compressed air bores 301 and 311 is subjected to compressed airduring the feed-back of yarn 10 into the yarn holding device 8. Since inan embodiment with a torsion element 3 of such design, with two sets ofcompressed air bores 300/310 and 301/311, the yarn holding device 8 canbe at a relatively great distance from the torsion element 3 inthreading position II for the threading of the fed-back yarn, wherebythe yarn 10 extends at a favorable angle to the torsion element 3 afterthe torsion element 3 has been returned into its spinning position I, nocomplicated drives for the yarn holding device 8 are needed.

According to FIG. 5 the torsion element 3 is associated with two stops34 and 35 of which the stop 34 determines the spinning position I andthe other stop 35 determines the threading position II of the torsionelement 3. This second stop 35 can here be installed on the piecingcarriage 9 so that it is attributed to the spinning station beingserviced during piecing, so that a separate stop 35 need not be providedfor each spinning station. Each stop 34 and 35 is equipped with anintake opening 340 or 350 for compressed air. The intake opening 340 forcompressed air is here installed in the stop 34 so that it is connectedto the compressed air openings 300 and 310 of the torsion element 3 whenthe latter is in spinning position I, while the intake opening 350 forcompressed air is installed in the stop 35 so that it matches thecompressed air openings 301 and 311 when the torsion element 3 is inthreading position II.

The compressed air is here controlled by means of a valve 71 as shown inFIG. 6.

In the embodiment shown in FIG. 5, each intake opening 340 or 350 forcompressed air is equipped with a check valve 341 or 351 which is openedwhen the torsion element 3 is applied against the corresponding stop 34or 35, and closes automatically when said torsion element 3 is liftedoff from said stops 34 or 35. It is thus no longer necessary to providefor separate control through control device 7 (as is the case with valve71 shown in FIG. 6).

We claim:
 1. A method for piecing after a thread break on a spinningdevice using a pneumatic torsion element for spinning into yarn rovingfed thereto with a drafting means having pairs of rolls, said methodcomprising the steps of:sensing breakage of yarn being fed to a windingmeans for winding yarn from said pneumatic torsion element; responsiveto such yarn breakage sensing, stopping roving being forwarded towardssaid pneumatic torsion element, while operating said winding means forfeeding back an end of yarn from said winding means and then retainingsuch yarn end in a yarn holding device adjacent said drafting means;removing a forward end of roving stopped in said drafting means andrendered unsuitable for piecing due to stoppage thereof, while treatingthe fed-back yarn end retained in said yarn holding device; during saidremoving step, restarting yarn winding with said winding means, while notwisting action is exerted on said yarn with said pneumatic torsionelement; and responsive to the position of said fed-back yarn end,bringing the yarn formerly retained in said yarn holding devicelaterally into said drafting means while operating same for feedingroving to said pneumatic torsion element and re-instating twistingaction therein; whereby the treated yarn end and roving unaffected bythe previous stoppage thereof are fed together into said pneumatictorsion element as the torsion effect thereof is restarted, to betwisted into yarn having even and unobtrusive piecing joints.
 2. Methodas in claim 1, wherein the yarn is initially drawn off through thetorsion element without any torsion effect being exerted by same uponthe yarn, termination of the removal of roving and resumption of thefeeding of roving to the torsion element is controlled as a function ofthe position of said fed-back yarn end, said roving subsequently beingsubjected together with the drawn-off yarn to restart of the twistingeffect with said torsion element.
 3. Method as in claim 1, whereinduring subsequent feeding of roving, the yarn is introduced laterallyinto the closed clamping line of a pair of output rolls of the draftingmechanism, and is fed to the torsion element at a speed determined bythe rotational speed of such pair of exit rolls.
 4. Method as in claim1, wherein the yarn to be brought together with the roving is retainedpneumatically after resumption of yarn draw-off to prevent uncontrolleddraw-off thereof and is furthermore braked mechanically until part of itis brought together with the roving.
 5. Method as in claim 1, whereinsuch treating includes cutting the fed-back yarn end to a defined lengthbefore having it brought together with the roving.
 6. Method as in claim5, further characterized in that the position of the end of the yarn inthe process of being fed together with said roving is sensed and in thatfurther operating cycles are controlled as a function of the sensedposition of the yarn end.
 7. A device for piecing to a spinningapparatus having a controllable pneumatic torsion element for twistingroving fed thereto into yarn, winding means for alternately taking upyarn from said torsion element and feeding back a free yarn end to suchtorsion element to form fed-back yarn, and drafting means for feedingroving to torsion element, said device comprising:suction means,adjacent the drafting means and the intake of the torsion element, forcontrollably removing roving therefrom; roving braking means, adjacentthe drafting means and upstream from said suction means, forcontrollably stopping roving in the drafting means; yarn monitoringmeans, adjacent the yarn path between the torsion element and the bobbinmeans, for outputting a signal responsive to breakage of such yarn;piecing control means, responsive to said yarn breakage signal, forsuccessively operating said roving braking means so as to stop feedingroving to the torsion means, said suction means so as to remove aportion of the roving forward end rendered unsuitable for piecing bysuch stoppage, and said roving braking means so as to re-start feedingof roving to the torsion element together and combined with yarnfed-back to the upstream side of the torsion element by said windingmeans; and pneumatic yarn holding means including yarn end monitoringmeans therein for selectively holding a fed-back yarn end adjacent thedrafting means and sensing the presence of a yarn end thereat,respectively, sensing thereof being used as an input to said piecingcontrol means for selectively operating said roving braking means andsaid torsion element for providing the torsion effect thereof so thattiming of the roving feeding re-start and release of the yarn end iseffected for entry of the roving and yarn end together into the torsiondevice as the torsion effect restarts.
 8. A device as in claim 7,wherein said pneumatic yarn holding means further includes a yarn brakefor selectively holding yarn therein initially during yarn draw-offduring piecing of such yarn.
 9. A device as in claim 8, wherein saidyarn brake may be selectively moved under control of said piecingcontrol means in and out of the path of yarn extending towards said yarnholding means.
 10. A device as in claim 7, wherein said yarn holdingmeans comprises a suction pipe, and further includes a yarn brakelocated thereinside for selectively holding yarn received inside saidsuction pipe.
 11. A device as in claim 7, further comprising apre-treatment means associated with said pneumatic yarn holding meansfor selectively pre-treating yarn held thereby.
 12. A device as in claim11, wherein said pretreatment means comprises a yarn cutting device forselectively trimming yarn received in said yarn holding means.
 13. Adevice as in claim 7, wherein a piecing carriage may be used forselectively transporting said piecing control means alongside saidspinning apparatus to any one of a plurality of spinning stationsthereof at which a yarn break has been sensed by yarn monitoring means.14. A device as in claim 13, wherein said piecing carriage alsoselectively transports said suction means, and means for actuating saidroving braking means, and further transports yarn holding means forselectively holding yarn fed back by said spinning apparatus in apiecing-ready position adjacent the respective drafting means at suchspinning station.
 15. A device as in claim 7, wherein said pneumatictorsion element, having an injection nozzle region followed by a torsionnozzle region, includes a first pair of compressed air bore sets ofcompressed air bore sets having a direction component in the directionof yarn draw-off, said first pair of sets being respectively segregatedbetween said injection nozzle and said torsion nozzle regions, andfurther includes a second pair of compressed air bore sets with adirection component in the direction of yarn feed-back, said second pairof sets being likewise segregated respectively between said regions. 16.A device as in claim 15, further comprising:first stop means associatedwith said torsion element for determining a spinning position thereof,said first stop means being provided with a first compressed air intakeopening connectable to said first pair of compressed air bore sets; andsecond stop means associated with said torsion element for selectivelydetermining a threading position thereof, said second stop means beingprovided with a second compressed air intake opening connectable to saidsecond pair of compressed air bore sets.
 17. A device as in claim 16,wherein said compressed air intake openings are each respectivelyfurther provided with a check valve which is actuated so as to be openedwhenever said torsion element is interactive with the corresponding stopmeans.
 18. A device as in claim 16, wherein a piecing carriage isadapted for traveling alongside said spinning apparatus and selectivelyinteracting with any spinning station thereof where a yarn breakage issensed, and further wherein said piecing carriage selectively transportssaid second stop means to any one of such spinning stations.
 19. Adevice as in claim 7, further comprising a suction nozzle situated justdownstream from said torsion element and adjacent the path of yarnbetween said torsion element and the winding means, said suction nozzlebeing selectively actuated for removing loose fibers and fly from thetorsion element whenever spinning operation is interrupted.
 20. Aspinning apparatus having a controllable pneumatic torsion element fortwisting roving fed thereto into yarn, drafting means for feeding rovingto said torsion element, and winding means for alternately drawing offand taking up yarn from said torsion element, and feeding back a freeyarn end to such torsion element to form fed-back yarn for piecing, saidtorsion element having an injection nozzle region followed by a torsionnozzle region, and including a first pair of compressed air bore setshaving a direction component in the direction of yarn draw-off, saidfirst pair of sets being respectively segregated between said injectionnozzle and said torsion nozzle regions, and including a second pair ofcompressed air bore sets with a direction component in the direction ofyarn feed-back, said second pair of sets being likewise segregatedrespectively between said regions.
 21. Apparatus as in claim 20, furthercomprising:first stop means associated with said torsion element fordetermining a spinning position thereof, said first stop means beingprovided with a first compressed air intake opening connectable to saidfirst pair of compressed air bore sets; and second stop means associatedwith said torsion element for selectively determining a threadingposition thereof, said second stop means being provided with a secondcompressed air intake opening connectable to said second pair ofcompressed air bore sets.
 22. Apparatus as in claim 21, wherein saidcompressed air intake openings are each respectively further providedwith a check valve which is actuated so as to be open whenever saidtorsion element is interactive with the corresponding stop means. 23.Apparatus as in claim 21, wherein a piecing carriage is adapted fortraveling alongside said spinning apparatus and selectively interactingwith any spinning station thereof where a yarn breakage is sensed, andfurther wherein said piecing carriage selectively transports said secondstop means to any one of such spinning stations.
 24. Apparatus as inclaim 20, further comprising:a suction nozzle situated just downstreamfrom said torsion element and adjacent the path of the yarn between saidtorsion element and said winding means, said suction nozzle beingselectively actuated for removing loose fibers and fly from the torsionelement whenever spinning operation is interrupted.